WHAT JUST HALPPENED!?

Hi guys, so this is my first post and I'll get straight to it. So basically I've been trying to astral project for the past three days with not much success (I hadn't even gotten to the "vibration stage" yet) but today I tried again with no success and eventually got tired and said I would sleep and try again in the morning. So I went to sleep and I think I fell asleep but the next thing I knew I was awake and my body was vibrating (when I say vibrating I mean literally shaking like I was on a roller coaster) i could also hear the loud noise in my head which sounded like a train screeching and a roller coaster ride happening at the same time, I didn't panic as I knew this was a good sign, this lasted for around 30seconds then stopped completely. At this point I knew I had to separate my body which was surprisingly easy, I just thought about getting up and it happened.

Now for the interesting part, once I had separated I couldn't see properly, as in everything was so dark I could barely see the outlines of my room, I also couldn't move properly it was as if my body weighed 1000pounds. I could also hear a very strange almost scary growling type sound coming from the corner of my room (but I couldn't see so I didn't know what it was) I assumed it was a negative entity but I didn't fear it, I went to approach the sound so I could tell the entity to leave (it was very hard to move) once I got there I tried to speak to tell it to leave but I couldn't, whenever I tried to talk only a very quiet mumbling sound came out, at this point I think I panicked and suddenly returned to my body. This all lasted about 10-15 seconds. Also during this time I could still feel my physical body and I could feel my physical eyes closed even though I could feel and move my astral body,it was quite strange.

Can anyone tell me what happened, and how can I experience this again; this OBE wasn't intentional but I went along with it, how can I make it happen when I try to do it ?
Sorry for the long story but I just want to know what happened and how I can have a proper OBE next time when I intend to do it. Thanks.